The present invention is directed to power regulating circuits, also called converters and power supplies, and more specifically to a constant-current type of series-switching regulator.
Series-switching regulators have several advantages over other types of non-switching regulators and shunt-type switching regulators. The efficiency of power conversion is inherently better in a series-switching arrangement. Efficiency is particularly important in moderate and high power applications since internal overheating of the regulator can result in inefficient circuits. The overall efficiency for series-switching regulators is typically 80-85%.
There are two different techniques used in series switching regulators to control the transfer of power to the load. One design uses a separate multivibrator (oscillator) to control the switching rate of the series-regulator switch. A feedback signal from the regulator output circuit indirectly adjusts the waveform of the multivibrator, which in turn sets the duty cycle of the switched input power. The switched power signal is usually integrated by a lowpass filter thereby providing a steady flow of power into the load.
The series-switching regultor switch using a separate multivibrator has the disadvantage of being difficult to control since multivibrators generally prefer to operate at a fixed duty cycle. Also, the stability of the entire regulator circuit can be a problem under no load or full load conditions. Consequently, this design tends to be complex and uneconomical, considering the added circuitry for stabilization of the overall regulator and control of the multivibrator.
Another control technique used in switching regulators is known as the self-oscillating technique. In the self-oscillating design, the power needs of the output automatically determine the switching rate of the switching regulator. This technique has the advantage of not requiring separate multivibrators, and regulators using this design have a faster response to changes in the load termination. There is less chance of damage to the regulator circuitry if it is able to respond rapidly to changes in load. This feature is particularly important if extreme changes in the load termination are possible. Usually, the self-oscillating technique is used for step-down voltage applications for reasons of efficiency. Further, the output voltage polarity is the same as the input unless a separate inverter circuit is used at the output of the regulator This additional circuitry tends to add expense, complexity, and inefficiencies.